This invention relates to a wheel. More specifically, this invention relates to a wheel which can easily go up and down stairs.
The Japanese Unexamined Patent publication No. 301459/H1 (1989) discloses a wheel which is capable of going up and down stairs (hereinafter referred to as xe2x80x9cprior art 1).
FIG. 10 is schematic views of a wheel 100 of the prior art 1. The reference numeral 110 is a cart. An axle 111 is secured horizontally to a lower part of the cart 110. A wheel 100 is journaled on each end portion of the axle 111 so as to be freely rotatable.
The wheel 100 has a cross-shaped rotator 104, which is journaled freely rotatably on the axle 111. The rotator 104 has four rollers 108A, 108B, 108C, and 108D, each roller journaled on one of the four tips of the rotator 104 so as to be freely rotatable.
Accordingly, as the rotator 104 of the wheel 100 rotates on the axle 111, the rollers 108A to 108D revolve around the axle 111.
Referring to FIG. 10, the movement of the wheel 100 going up stairs will be described next.
The letter xe2x80x9cAxe2x80x9d indicates the riser of the first step of a stairway; xe2x80x9cBxe2x80x9d the tread; xe2x80x9cCxe2x80x9d the top corner.
As shown in FIG. 10(I) , while the cart 110 is moving on the surface of a road, the rollers 108A and 108B roll on the road surface and the rollers 108D and 108C are positioned above the rollers 108A and 108B, respectively.
As shown in FIG. 10(I), when the cart 110 reaches a stairway, the front lower roller 108B comes in contact with the riser xe2x80x9cAxe2x80x9d of the first step.
As shown in FIG. 10(II) , when the cart 110 is pulled up forward, the wheel 100 turns forward about the roller 108B, which remains pressed against the riser xe2x80x9cAxe2x80x9d of the first step, for the rotator 104 is rotatable on the axle 111. Accordingly, the front upper roller 108C moves onto the tread xe2x80x9cBxe2x80x9d of the first step beyond its top corner xe2x80x9cCxe2x80x9d.
As shown in FIG. 10(III), when the cart 110 is further pulled up forward, the roller 108C rolls forward on the tread xe2x80x9cBxe2x80x9d and the roller 108B rolls on the riser xe2x80x9cAxe2x80x9d upward.
Thus, the rotator 104 can be turned on the axle 111 and pulled up forward, and hence the wheel 100 and the cart 110 can be pulled up forward.
As shown in FIG. 10 (IV), when the cart 110 is still further pulled up forward, the roller 108B goes beyond the top corner xe2x80x9cCxe2x80x9d and gets onto the tread xe2x80x9cBxe2x80x9d. Thus, the whole wheel 100 and hence the cart 110 get onto the tread xe2x80x9cBxe2x80x9d of the first step.
As described above, the wheel 100 of the prior art 1 can go up a stairway by turning the rotator 104 on the axle 111 and rolling the front lower roller and the front upper roller on the riser xe2x80x9cAxe2x80x9d and the tread xe2x80x9cBxe2x80x9d, respectively, of each step.
The Japanese Unexamined Utility Model publication No. 191669/S57 (1982) discloses another wheel which is capable of going up and down stairs (hereinafter referred to as xe2x80x9cprior art 2xe2x80x9d).
FIG. 11 is schematic views of a wheel 120 of the prior art 2. The wheel 120 comprises a rectangular rotary plate 124 and four rollers 128A, 128B, 128C, and 128D which are supported by brackets at the four corners of the rotary plate 124. Each of the four sides 125 of the rotary plate 124 is concaved in an arc-like shape.
In the same way as the wheel 100 of the prior art 1, the wheel 120 gets on a step by putting the front upper roller 128C on the tread xe2x80x9cBxe2x80x9d of the step and rolling it on the tread xe2x80x9cBxe2x80x9d forward and, at the same time, rolling the front lower roller 128B upward on the riser xe2x80x9cAxe2x80x9d of the step. Although the rotary plate 124 is different from the rotator 104 of the wheel 100 in shape, the principle of the wheel 120 is the same as that of the wheel 100.
The wheels 100 and 120 of the prior arts 1 and 2 have the following shortcomings (1) to (4).
(1) In case of the wheel 100 of the prior art 1, when the rotator 104 turns about the roller 108B, the roller 108C comes in contact with the tread xe2x80x9cBxe2x80x9d at a relatively high speed, as shown in FIGS. 10(I) and 10(II). Accordingly, when the roller 108C bumps against the tread xe2x80x9cBxe2x80x9d, it gives rise to a large shock. Thus, the cart 110 is exposed to large shocks and vibration while it is pulled up the stairway. The goods in the cart 110 may be damaged. In addition, the hands pulling the cart 110 are exposed directly to the unpleasant vibration of the cart 110.
(2) The wheel 100 of the prior art 1 cannot be pulled up a stairway without risers xe2x80x9cAxe2x80x9d because it cannot be turned about the roller 108B to put the roller 108C on the tread xe2x80x9cBxe2x80x9d. Even if the roller 108C can be put on the tread xe2x80x9cBxe2x80x9d, the roller 108B cannot goes up toward the tread xe2x80x9cBxe2x80x9d because there is not a riser xe2x80x9cAxe2x80x9d for the roller 108B to roll on.
(3) In case of the wheel 120 of the prior art 2, because each of the four sides of its rotary plate 124 is concaved in an arc-like shape, the roller 128B can be raised by leaning the side 125 on the top corner xe2x80x9cCxe2x80x9d of a step and turning the rotary plate 124 forward about the top corner xe2x80x9cCxe2x80x9deven if the stairway has no risers xe2x80x9cAxe2x80x9d, as shown in FIG. 11 (II). However, in order to pull up the roller 128B onto the tread xe2x80x9cBxe2x80x9d, the wheel 120 has to be moved by sliding the side 125 on the top corner xe2x80x9cCxe2x80x9d. Because the side 125 has no guiding function, there occurs large resistance between the wheel 120 and the stairway. Accordingly, although the wheel 120 can be pulled up a stairway without risers xe2x80x9cAxe2x80x9d, it requires large force to pull the cart up the stairway.
(4) In case that the wheel 120 of the prior art 2 is pulled up a stairway with risers xe2x80x9cAxe2x80x9d, a side 125 is slid on the top corner xe2x80x9cCxe2x80x9d of each step and the front lower roller 128B comes in contact with the top corner xe2x80x9cCxe2x80x9d of said step. At this time, if the center of the front lower roller 128B is lower than the tread xe2x80x9cBxe2x80x9d of said step, the front lower roller 128B runs almost horizontally into the riser xe2x80x9cAxe2x80x9d of said step and its horizontal movement ceases. Accordingly, when the front lower roller 128B runs into the riser xe2x80x9cAxe2x80x9d of said step, it causes a large shock. The goods in the cart may be damaged by the shock and vibration. In addition, the hands pulling the cart are exposed to the vibration of the cart.
Besides, the horizontal component of the pull force is wasted, just used to bump the front lower roller 128B against the riser xe2x80x9cAxe2x80x9d of said step. Only the vertical upward component of the pull force is made use of for raising the center of the front lower roller 128B above the tread xe2x80x9cBxe2x80x9d of said step. Thus, it requires large force to pull the cart up the stairway.
In accordance with the above, the object of the present invention is to provide a wheel which enables us to carry a movable body equipped with two units of the wheel easily up a stairway, even without risers, with small pull force, causing small shocks and vibration.
According to the first aspect of the present invention, there is provided a wheel comprising (i) an axle secured to a movable body, (ii) a rotator journaled on the axle so as to be freely rotatable and having at least three apexes disposed rotationally symmetrically around the axle, and (iii) rollers, each roller being mounted on one of the apexes of the rotator so as to be freely rotatable. Each side between apexes of the rotator is provided with a guiding surface which has small frictional resistance and is slidable.
According to the second aspect of the present invention, there is provided the wheel of the first aspect wherein each guiding surface is concaved in an arc-like shape.
According to the third aspect of the present invention, there is provided the wheel of the first or second aspect wherein (i) the point of intersection of each guiding surface and the periphery of one of the two rollers defining said guiding surface is positioned outside of the straight line which extends from the center of the roller to be tangent to the periphery of the other roller from the outside of the wheel and (ii) the angle between each end portion of each guiding surface and the straight line which is, at the point of intersection of said end portion of said guiding surface and the periphery of the roller corresponding to said end portion, tangent to the periphery of the roller is small.
The advantages offered by the first aspect of the present invention are as follows. While the movable body equipped with two units of the wheel of the invention is moved on the surface of a road, two rollers of each wheel roll on the road surface. Accordingly, the movable body can be moved smoothly on the road surface. When it comes to a stairway, by putting the forward-facing guiding surface of the rotator of each wheel into contact with the top corner of each step and pulling up the movable body forward, the rotator of said wheel can be slid on the top corner of said step and moved upward, for said guiding surface are slidable and has small frictional resistance. Therefore, even if the stairway is of a no-riser type, by putting the forward-facing guiding surface of the rotator of each wheel into contact with the top corner of each step, the movable body can be carried up the stairway with relatively small force. Moreover, every time the movable body climbs a step, the rotator of each wheel turns by the central angle between rollers to face its next guiding surface forward so that it can be put into contact with the top corner of the next step. Thus, the movable body can be carried up the stairway step by step successively.
The advantages offered by the second aspect of the present invention are as follows. Because each guiding surface of each wheel is concaved in an arc-like shape, the angle between the tangent to the point of said guiding surface where it is in contact with the top corner of a step and the tread of the step is small. Therefore, the component of the pull force to pull the rotator up forward is large. Accordingly, the movable body can be carried up the stairway with relatively small pull force. In addition, because the rotator of each wheel turns about the top corner of each step, the distance between the front upper roller of said wheel and the top corner of said step becomes small and, hence, the turning speed of the front upper roller of said wheel becomes small. Accordingly, the shock to be caused by putting the front upper roller of each wheel on the tread of each step can be reduced. Moreover, because the contact point between the top corner of each step and a guiding surface of the rotator of each wheel moves backward on said guiding surface while said rotator turns forward continuously about the top corner of said step, the front upper roller of said rotator can be put on the tread of said step without causing a large shock. Thus, the movable body can be carried up the stairway step by step smoothly and successively, causing relatively small shocks and vibration.
The advantages offered by the third aspect of the present invention are as follows. While the front upper roller of each wheel is pulled up forward onto the tread of the next step and rolling forward on the tread, the front lower roller of said wheel is pulled upward and the point of intersection of the guiding surface between the front upper and lower rollers and the periphery of the front lower roller is drawn toward the top corner of the next step. When the point of intersection of said wheel comes in contact with the top corner of the next step, the center of the front lower roller of said wheel is positioned higher than the top corner of the next step. Accordingly, the horizontal component of the pull force applied to the movable body acts to turn the front lower roller of said wheel upward about the top corner of the next step. Thus, compared with the force otherwise necessary to pull up the front lower roller of each wheel onto the next step, it can be pulled up with smaller force. Moreover, because the front lower roller of each wheel turns forward when it comes in contact with the top corner of the next step, the shock can be reduced. In addition, each guiding surface of each wheel connects smoothly with the peripheries of the rollers defining said guiding surface. Therefore, the shock and vibration to de caused by the front lower roller of each wheel coming in contact with the top corner of the next step can be reduced and said front lower roller can be moved smoothly from the riser to the tread of the next step.